This invention relates to new elastomeric articles having enhanced ozone degradation resistance due to the presence therein of novel triazine compounds. Specifically, tris(N-alkyl-p-phenylenediamino)-1,3,5-triazine compounds are used to protect highly unsaturated rubber polymers in the elastomeric body of the articles of manufacture. The exterior surfaces of the articles are the areas subject to ozone degradation: therefore, it is most advantageous to utilize the compounds in the exterior elastomeric layers of the article that are exposed to the environment. The types of elastomeric articles in which the invention is most useful are those subject to severe dynamic flexing during the periods of ozone exposure. Articles such as conveyor belts, power transmission belts, hoses, fluid springs, roofing membranes, bushings, expansion joints, vibration dampers, wire and cable jacketing.
It is well known that ozone causes surface cracking of conventional highly unsaturated rubber vulcanizates when the rubber is placed under strain in an ozone environment. The most severe deterioration occurs when a small number of cracks are formed which grow rapidly into deep, disruptive fissures. These ozone cracks seriously shorten the serviceable life of the article.
Chemical antiozonants have been developed which retard the formation of the ozone cracks occuring under static and dynamic conditions. Examples of antiozonants in common use include: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine; N-phenyl-N'-isopropyl-p-phenylenediamine; N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine; N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine; N-phenyl-N'-cyclohexyl-p-phenylenediamine; mixed diaryl-p-phenylenediamines; N,N'-diphenyl-p-phenylenediamine; N,N'-di-beta-naphthyl-p-phenylenediamine: N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine; N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine; N,N'-bis(1-methylheptyl)- p-phenylenediamine; N-phenyl-N'-p-toluenesulfonyl-p-phenylenediamine and blends of these materials.
The use of these well known paraphenylenediamine materials has improved ozone protection under both static and dynamic conditions, however, even the best of the class just described have a very strong tendency to both stain and discolor. The term "stain" or "staining" is herein used to describe the characteristic of a material objectionable in most rubber articles to diffuse through a polymeric substrate and discolor the adjacent surface. This diffusion staining is highly objectionable in most rubber articles, particularly light color articles.
Waxes have been long utilized to inhibit ozone cracking in articles under stress in static condition by incorporating the wax into the rubber compound prior to vulcanization. The wax functions by migrating to the surface of the rubber article to form a film which acts as a physical barrier to the ozone attack. However, during dynamic flexing in service, the wax film is cracked or disrupted and the tendency is for the article to exhibit fewer and more severe ozone cracks than if no wax had been incorporated. Therefore, for many service conditions, the use of wax is impractical due to the dynamic conditions under which the article is expected to perform.
An object of this invention is to provide rubber articles which are more effectively protected against ozone attack at their exterior peripheral surfaces. A further object is to provide ozone protection in a static condition at very low levels and to protect the rubber article during extended aging conditions against ozone attack. Yet another object is to produce a compound which slowly diffuses and does not produce an objectionable brown bloom on the surface of the compound.
The novel arylenediamine substituted triazine compounds of the invention have provided exceptional long term ozone protection under static conditions without using wax. An advantage of the substituted triazine compounds is that it produces a substantially non-staining antiozonant of high molecular weight. A further advantage is that it slowly blooms to the surface of the rubber article. A further advantage is that the triazine compounds of the invention provide outstanding dynamic protection without the use of waxes preferably by blending said triazine compounds with other known antiozonants and antioxidants. Another advantage is that the compounds do not tend to increase scorchiness of the compounded rubber stock in which it is used. This improves processing safety over other paraphenylenediamine antiozonants.